In recent years, as the technology for computers, cameras, image processing and so forth have made progress, a high sense of reality is required for a display apparatus. For a display apparatus achieving a high sense of reality, a stereoscopic display apparatus providing an observer's right and left eyes with parallax images or a display apparatus on which a superfine image of 4K or 8K is displayed has been developed.
While the stereoscopic display apparatus includes an eyeglass type employing special eyeglasses and a naked-eye type requiring no eyeglasses as a technique for sending different images, respectively, to the right and left eyes of an observer, the development of the naked-eye type has been expected in terms of the burden of wearing eyeglasses.
Generally, in the stereoscopic display apparatus of the naked-eye type, a unit pixel for displaying a viewpoint image for the left eye and the right eye on a display panel is provided, to sort corresponding images to the right and left eyes of an observer by an optical member such as lenticular lens or parallax barrier. This requires unit pixels constituting viewpoint images by the number corresponding to the number of viewpoints, and an even larger number of pixels (the number of pixels in a regular display×the number of viewpoints) is required for stereoscopic display with an image quality having the smoothness and resolution of an image equal to that in a regular (two-dimensional) display, in order to achieve an increased sense of reality.
However, the increase in the number of pixels in a display panel causes the increase in the amount of display data to be sent from the signal processing unit in the display apparatus to the display panel, which further increases the transfer frequency of display data and the frequency of clock signals. As the frequency is higher, data signals and clock signals have larger distortion, causing a problem of degrading in the display quality and increasing in the power consumption by a driver IC due to the ground (GND) being unstable. Moreover, if display data signals in a data bus are changed at the same timing, the power line is significantly affected, which will cause noise in a driver circuit, deteriorating the display quality and increasing the power consumption. This phenomenon is generally called simultaneous switching noise.
The above-described influence of signal distortion, power-supply variation and noise on the display quality due to the increase in the drive frequency (display data transfer frequency and clock frequency) associated with the recent increase in the resolution (increase in the number of pixels) has been a cause to decelerate the development of the naked-eye type stereoscopic display apparatus. For example, a problem arises in that the stereoscopic optical characteristic (3D crosstalk) cannot be correctly evaluated. In general, a display panel of a naked-eye display apparatus supplies data to unit pixels respectively constituting different viewpoint images by the adjacent data lines. In order to evaluate the stereoscopic optical characteristic (3D crosstalk), a display pattern is used which maximizes the difference in gradation levels, i.e. gradation difference, of different viewpoint images (for example, black for the right-eye image and white for the left-eye image). This display pattern causes a simultaneous switching noise because each bit in the data bus are simultaneously changed. The noise further affects the result of measurement of the optical characteristics of an optical element which separates viewpoint images when the luminance is lowered in the display panel. This causes the stereoscopic optical characteristics (3D crosstalk), which are basically decided by the pixel layout and the characteristics of optical elements, to include the problem of a drive circuit, which hinders a correct evaluation.
Moreover, the above-described problems of signal distortion, power-supply variation and noise due to the higher drive frequency is caused also in a two-dimensional (2D) display apparatus for displaying superfine images of 4K or 8K as the number of pixels is increased, possibly deteriorating the display quality.
As a technique for suppressing the transfer frequency of the display data described above, a technique of dividing data signals to be sent to the display panel, to multiple buses. Furthermore, the technique of suppressing the peak of the noise components by shifting the phase of data for each bus, which is divided data signal, is known for suppressing simultaneous switching noise.
For example, Japanese Patent Application Laid-Open Publication No. H6-289822 discloses a method of dividing display data into two pieces and transferring one of the data pieces with a polarity opposite to that of the other data piece. Moreover, Japanese Patent Application Laid-Open Publication No. H11-249622 discloses a technique in which an input data signal is divided into multiple output signals and a phase difference is provided between the divided output signals so as to reduce the number of simultaneous changes of the output signals. Furthermore, Japanese Patent No. 3993297 discloses a method of outputting data signals with multiple stages of phases different for each data group (the RGB data group is divided into red(R), green(G) and blue(B), for example), and changing the phase difference randomly in terms of time.